Aiming at the problems of low reconciliation efficiency and key leakage of the classical Cascade protocol, an improved Cascade protocol aided by fluctuation error quantization was proposed. Before reconciliation, the statistical characteristics of the fluctuation difference of channel magnitude feature of legitimate nodes were studied and a fluctuation error quantization method was proposed by using it. Based on the proposed quantization method, an improved Cascade protocol was designed by parity grouping and partitioning reconciliation. Numerical results demonstrate that the proposed improved Cascade protocol effectively improve the reconciliation efficiency, reduces the computational complexity required for information reconciliation and the possibility of key information leakage at the cost of partial reconciliation success rate. In addition, compared with the existing key generation schemes, the key generation scheme based on the proposed improved Cascade protocol has a lower key inconsistency rate and a higher key generation rate.